1. Field of the Invention
The present invention relates to an image communication apparatus and system.
2. Description of the Related Art
In the case of using a conventional analog telephone circuit as a communication apparatus, the telephone itself can transmit only voice data, and all other types of data can be transmitted only at low speed.
Recently, however, as a result of progress in communication technology, semiconductor technology and optical technology, digital networks have been provided, which make it possible to transmit large quantities of data at high speed.
Such digital transmission has advantageous features in that, for example, the same level of data quality can be maintained without degradation during data transmission. Also, a particular transmission channel corresponding to the characteristics of the kind of transmitted data is not required, and therefore all types of media can be accommodated. Hence, it has become possible to perform transmission between complex multimedia terminals and, as a result, multimedia communication apparatuses are utilized in which a telephone can simultaneously transmit images as well as voice data.
International standardization by the ITU-T has intended to ensure that mutual communication can be performed between terminals which deal with voice data and image data, and service provisions, protocol provisions, and provisions for the configuration of multimedia multiplexed frames for AV (audiovisual) services, such as video telephones, video conferences, and the like using a digital network, have been announced as H.320, H.242, H.221 and H.261 as recommended by the ITU-T.
In H.221, the frame configuration, exchange of terminal capabilities, and code allocation of an FAS (Frame Alignment Signal) and a BAS (Bit Allocation Signal) in a communication mode in an AV series for 64 Kbits to 1920 Kbits are defined.
In H.242, protocols for the exchange of capabilities between AV terminals using a BAS, the switching of the communication mode, and the like are defined. In H.320, system aspects for all AV services are defined.
In the above-described recommendations, methods are provided for performing the communication of multimedia, comprising images, voice, data, and the like between terminals according to procedures, such as a sequence of in-channel exchanges of terminal capabilities using a BAS, a mode-switching sequence by assigning a communication mode and the like after setting of an end-to-end physical connection and in-channel establishment of synchronization using a FAS.
However, methods for changing the capabilities of a terminal in accordance with a new situation, and methods of selecting a communication mode within the range of exchanged capabilities are not provided.
In multimedia communication, the information transfer speed for voice information is determined by assigning a voice-encoding method, and the transfer speed for data information is determined by assigning the value of the transfer speed when data information is transferred. The transfer speed for image information is obtained by subtracting the transfer speed for voice transformation and the transfer speed for data information from the set information transfer speed of the entire communication channel. A coding method and image data transfer format is defined by H.261.
However, such conventional communication apparatus has certain problems. For example, in such conventional communication apparatus, it is not possible to change image format, because the image format of H.261 has been already defined.
In H.261 a selection is made between CIF (Common Intermediate Format) that is a high quality image, and QCIF (Quarter CIF) that is an ordinary quality image, therefore, the variable quality of an image cannot be changed.
The size of an input has to be enlarged or reduced in order to fit to the H.261 format when the size of the input image is different from that of H.261. Such enlarging or reducing may reduce the quality of the image.
In conventional communication apparatus, in order to transmit a combined image with a static image and a motion image, the static image and the motion image must be transmitted according to the H.261 format. In other words two frames have to be transmitted in order to combine the images.
At a receiving side, a received motion image is enlarged or reduced prior to being combined with the static image. Such a combining process requires more time than an ordinary process that does not need the combining process. Such an enlarging process causes an increase in the amount of information to be transmitted, therefore such an enlarging process causes inefficiency in communication.